Buggy code:
public class EngineDebugger extends EngineDriver implements EngineModeObserver , InterpreterListener { private ControlAPI capi = ( ( ControlAPI ) ( engine ) ) ; private WatchExpressionAPI wapi = new WatchExpressionAPI ( capi ) ; private Stack < ASMStorage > states = new Stack < ASMStorage > ( ) ; private ASMDebugTarget debugTarget ; private String sourceName ; private String specPath ; private Element currentAgent ; private int lineNumber ; private ASMStorage stateToDropTo ; private ASTNode stepOverPos ; private ASTNode stepReturnPos ; private ASTNode prevPos ; private Stack < Map < ASTNode , String > > ruleArgs = new Stack < Map < ASTNode , String > > ( ) ; private Set < ASMUpdate > updates = new HashSet < ASMUpdate > ( ) ; private IBreakpoint prevWatchpoint ; private boolean stepSucceeded = false ; private volatile boolean shouldStep = false ; private volatile boolean shouldStepReturn = false ; private volatile boolean shouldStepOver = false ; private volatile boolean shouldStepInto = false ; protected EngineDebugger ( boolean isSyntaxEngine ) { } public static EngineDebugger getRunningInstance ( ) { } @ Override public synchronized void stop ( ) { } @ Override public synchronized void pause ( ) { } @ Override public synchronized void resume ( ) { } public synchronized void setStepping ( boolean shouldStep ) { } public synchronized boolean isStepping ( ) { } public synchronized void stepOver ( ) { } public synchronized void stepInto ( ) { } public synchronized void stepReturn ( ) { } public ASMStorage [ ] getStates ( ) { } public String setValue ( String functionName , String expression ) { } public Element evaluateExpression ( String expression , ASMStorage storage ) throws ParserException , InterpreterException { } public boolean isStepFailed ( ) { <START_BUG> return ! ( stepSucceeded ) ; <END_BUG> } public boolean isUpdateConsistent ( ASMUpdate update ) { } public Set < ASMUpdate > getLastInconsistentUpdate ( ) { } public Set < ASMUpdate > getUpdates ( ) { } public int getStep ( ) { } @ Override protected void preExecutionCallback ( ) { } @ Override protected void postExecutionCallback ( ) { } @ Override public synchronized void updateStatus ( EngineDriverStatus status ) { } public static void newLaunch ( String abspathname , ILaunchConfiguration config ) throws CoreException { } public void dropToState ( ASMStorage stateToDropTo ) { } private void dropToState ( ) { } @ Override public void update ( EngineEvent event ) { } @ Override protected void handleError ( ) { } public void setDebugTarget ( ASMDebugTarget debugTarget ) { } public String getSpecPath ( ) { } private void waitForStep ( ASTNode pos ) { } private void onBreakpointHit ( ASTNode pos ) { } public void updateState ( ASTNode pos ) { } private boolean isUnvisited ( ASTNode pos ) { } private boolean isWatchpointHit ( FunctionRuleTermNode frNode ) { } private boolean isLineBreakpointHit ( ) { } @ Override public void beforeNodeEvaluation ( ASTNode pos ) { } @ Override public void afterNodeEvaluation ( ASTNode pos ) { } @ Override public void onRuleCall ( RuleElement rule , List < ASTNode > args , ASTNode pos , Element agent ) { } @ Override public void onRuleExit ( RuleElement rule , List < ASTNode > args , ASTNode pos , Element agent ) { } @ Override public void initProgramExecution ( Element agent , RuleElement program ) { } }

Fix:
return ( capi . getStorage ( ) . getLastInconsistentUpdate ( ) ) != null ;